Effects of a rock‐ramp fishway on summer fish assemblage in a Lake Huron tributary

The use of nature‐like fishways to increase ecosystem connectivity has increased in recent years, but their effectiveness has rarely been evaluated. A rock ramp was constructed in the Shiawassee River in 2009, and post‐construction effects (2011–2012) were evaluated on the summer fish assemblage by comparing fish assemblage composition to a nearby free‐flowing river and a nearby river with a dam. Patterns of fish species richness, mean catch‐per‐unit‐effort and proportional abundance in reaches upstream and downstream of the rock ramp, dam and comparable sites in the free‐flowing river were evaluated. Overall, species richness by site and proportional abundance in the rock‐ramp river were more similar to the free‐flowing river, while species richness by reach was more similar to the dammed river. These findings suggest that the rock ramp has improved connectivity for the summer fish assemblage, but has not fully restored conditions to the level observed in a free‐flowing river.     

Restoring connectivity for migratory native fish in a New Zealand stream: effectiveness of retrofitting a pipe culvert

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A quantitative assessment of fish passage efficiency

In an attempt to restore the connectivity of fragmented river habitats, a variety of passage facilities have been installed at river barriers. Despite the cost of building these structures, there has been no quantitative evaluation of their overall success at restoring fish passage. We reviewed articles from 1960 to 2011, extracted data from 65 papers on fish passage efficiency, size and species of fish, and fishway characteristics to determine the best predictors of fishway efficiency. Because data were scarce for fishes other than salmonids (order Salmoniformes), we combined data for all non‐salmonids for our analysis. On average, downstream passage efficiency was 68.5%, slightly higher than upstream passage efficiency of 41.7%, and neither differed across the geographical regions of study. Salmonids were more successful than non‐salmonids in passing upstream (61.7 vs. 21.1%) and downstream (74.6 vs. 39.6%) through fish passage facilities. Passage efficiency differed significantly between types of fishways; pool and weir, pool and slot and natural fishways had the highest efficiencies, whereas Denil and fish locks/elevators had the lowest. Upstream passage efficiency decreased significantly with fishway slope, but increased with fishway length, and water velocity. An information‐theoretic analysis indicated that the best predictors of fish passage efficiency were order of fish (i.e. salmonids > non‐salmonids), type of fishway and length of fishway. Overall, the low efficiency of passage facilities indicated that most need to be improved to sufficiently mitigate habitat fragmentation for the complete fish community across a range of environmental conditions.     

Unintended consequences and trade‐offs of fish passage

We synthesized evidence for unintended consequences and trade‐offs associated with the passage of fishes. Provisioning of fish passageways at dams and dam removals are being carried out increasingly as resource managers seek ways to reduce fragmentation of migratory fish populations and restore biodiversity and nature‐like ecosystem services in tributaries altered by dams. The benefits of provisioning upstream passage are highlighted widely. Possible unwanted consequences and trade‐offs of upstream passage are coming to light, but remain poorly examined and underappreciated. Unintended consequences arise when passage of native and desirable introduced fishes is delayed, undone (fallback), results in patterns of movement and habitat use that reduce Darwinian fitness (e.g. ecological traps), or is highly selective taxonomically and numerically. Trade‐offs arise when passage decisions intended to benefit native species interfere with management decisions intended to control the unwanted spread of non‐native fishes and aquatic invertebrates, or genes, diseases and contaminants carried by hatchery and wild fishes. These consequences and trade‐offs will vary in importance from system to system and can result in large economic and environmental costs. For some river systems, decisions about how to manage fish passage involve substantial risks and could benefit from use of a formal, structured process that allows transparent, objective and, where possible, quantitative evaluation of these risks. Such a process can also facilitate the design of an adaptive framework that provides valuable insights into future decisions.     

Remediation of upstream passage for migrating Galaxias (Family: Galaxiidae) through a pipe culvert

Movement through streams is critical for the maintenance of diadromous fish populations. Numerous fish passage improvement techniques exist, and knowledge of their effectiveness is required to conserve target species. An existing 70‐m pipe culvert was considered a barrier to the passage success of young‐of‐year (YOY) Galaxias spp. as a result of high water velocity (0.9 m/s). Water velocity in the pipe culvert was reduced by installing a concrete weir downstream of the culvert. A lateral ridge rock‐ramp fishway was installed to provide for the passage of fish over the weir, and baffles were installed in the upstream portion of the culvert to provide refuge from higher water velocity at this location. A BACI design was used to determine whether passage success, measured using a mark–recapture technique, improved as a result of the remediation works. The probability of successful passage of YOY Galaxias spp. through the culvert increased from 0.03 to 0.41 following remediation works and was similar to levels observed at a control site (0.33). The success of the fishway and baffles at this culvert provides an important case study for managers to adopt this technique to improve fish passage on a broader scale and range of other sites.     

Spatiotemporal patterns of fish community composition in Great Lakes drowned river mouths

Freshwater river mouths in large lakes are centres of biological activity, yet little is understood about the spatial and temporal dynamics of fish communities in these systems. In the Laurentian Great Lakes, we sampled littoral fishes over 3 years in six drowned (i.e., protected) river mouths to: (i) quantify spatial (among river mouths) and temporal (among years) variation, (ii) evaluate associations with environmental conditions and (iii) assess spatial patterns of community similarity. We sampled 6787 fish representing 43 species over the course of the study. Multivariate analyses indicated that variation in fish species composition was more strongly partitioned among river mouths than among years. Fish communities across the six river mouths were partitioned into three groups, a pattern we attribute to variability in anthropogenic disturbance and environmental conditions. Canonical correspondence analysis showed that fish species composition was associated with specific conductivity, vegetation cover, turbidity and pH, suggesting species–environment relationships are similar to those shown for Great Lakes coastal wetlands. Finally, we found a negative relationship between geographic distance and community similarity, suggesting that dispersal and/or environmental gradients play a role in shaping these river mouth fish assemblages. We conclude that Great Lakes drowned river mouths can harbour diverse and spatially variable fish assemblages that are driven by a combination of local and regional factors.     

Movement ecology of imperilled fish in a novel ecosystem: River‐reservoir movements by razorback sucker and translocations to aid conservation

1. Reservoirs and associated river fragments are novel ecosystems not experienced by fishes in their evolutionary history, yet they are now commonplace across the globe. Understanding how fishes use these novel habitats is vital to conservation efforts in contemporary riverscapes.
2. Movement patterns of the endangered razorback sucker (Xyrauchen texanus) synthesized from tagging efforts in the upper Colorado River basin, USA, illustrate the applications of tagging technology and data sharing by multiple agencies to better understand the spatial ecology of large river fishes.
3. Tagging studies between 2014 and 2018 in Lake Powell and its two main tributary rivers, the Colorado (unfragmented) and San Juan (waterfall‐fragmented), were used to quantify movement of razorback sucker within this river–reservoir habitat complex. In addition, facilitated translocations of fish upstream of a waterfall barrier in the San Juan River were assessed in 2016–2017.
4. Extensive movement of fish occurred within and across river and reservoir habitats. Of 722 fish captured in the Colorado River arm of Lake Powell, 36% of re‐encounters occurred upstream in the Colorado or Green rivers, or fish dispersed through the reservoir and were detected in the San Juan River arm. Fourteen fish moved more than 600 km. In the San Juan arm of the reservoir, 29% and 20% of fish in 2017 and 2018, respectively, had moved ~30–40 km upstream below the waterfall in the San Juan River within a year. In 2016–2017, 303 fish were translocated upstream of the waterfall into the San Juan River, but 80% were re‐encountered downstream of the waterfall within a year.
5. Long‐distance movements by razorback sucker were common within and among rivers and reservoirs illustrating how large river fish, in general, might maintain population connectivity in highly altered ecosystems.

     

Increasing connectivity of Great Lakes tributaries: Interspecific and intraspecific effects on resident brook trout and brown trout populations

Understanding resident fish population responses to restored connectivity would enhance decision-making on dam removal and fish passage. Since such evaluations are limited in the Great Lakes region of North America, we compared abundance, survival, and growth of resident brook trout and brown trout between sets of Michigan streams where populations were or were not interacting with salmonid species that might be present if connectivity existed. We analysed data from 34 electrofishing index sites to compare resident trout populations between streams without versus with Great Lakes access (and migratory Pacific salmonids), and brook trout populations in Great Lakes inaccessible (land-locked) streams where brown trout were present versus absent. Great Lakes accessibility effects on fish density became increasingly positive for older age groups of brown trout while generally negative for all age classes of brook trout. Brown trout had consistently negative effects on brook trout density in land-locked streams. Increased connectivity had significant effects on annual survival for only one of seven trout age classes modelled, while intraspecific density-dependent effects on survival were significant in six models. Significant intraspecific effects on resident trout growth occurred for seven of eleven age classes examined. Negative interspecific effects of Great Lakes access on resident trout growth were most noticeable for age-0 and age-1 resident trout, age classes that likely compete with juvenile Pacific salmonids. Our findings provide a more robust understanding of how Great Lakes connectivity affects resident trout populations, highlighting negative influences of brown trout on brook trout and intraspecific density-dependent effects.     

Large‐bodied fish migration and residency in a flood basin of the Sacramento River,California, USA

River–floodplain complexes represent some of the most variable and diverse habitats on earth, yet they are among our planet's most threatened ecosystems. Use of these habitats by large‐bodied fishes is especially poorly understood, particularly in temperate regions. To provide insight into the factors that affect floodplain assemblages and migration, we sampled large‐bodied fishes with a fyke trap for 7 years in the Yolo Bypass, the primary flood basin of the Sacramento River, California. We collected a total of 18,336 individual fish comprised of 27 species, only 41% of which were native. Year‐round resident species white catfish Ameiurus catus, channel catfish Ictalurus punctatus and common carp Cyprinus carpio (all alien species) were the most abundant and comprised 74% of the total catch. Splittail Pogonichthys macrolepidotus (3.8%), white sturgeon Acipenser transmontanus (2.3%) and Sacramento sucker Catostomus occidentalis (1.1%) were the primary native species. We found that seasonal variation in water temperature and flood stage were important factors affecting the fish assemblage structure and the presence of migratory species. American shad Alosa sapidissima, an alien species, showed highest abundance during the early summer upstream migration, when temperatures were warmer. For native species, the abundances of white sturgeon, splittail, Sacramento pikeminnow Ptychocheilus grandis and Sacramento sucker were all highest during flood pulses. While our results suggest that flow alone is not sufficient to control alien species, the strong linkage between native fish migration and flow pulses highlights the importance of river–floodplain connectivity for the conservation of native fishes.     

Rapid response of fish and aquatic habitat to removal of a tidal barrier

1. River barrier removal is used increasingly as a conservation tool to restore lotic habitat and river connectivity, but evidence of its efficacy is incomplete. This study used a before–after methodology to determine the effects of removing a tidal-limit barrier on the fishes, macroinvertebrates, and habitats of an English coastal stream.
2. Following barrier removal, habitat diversity increased immediately upstream and remained similar downstream. Mobilized silt altered the substrate composition immediately downstream, but this was temporary as silt was flushed out the following winter. Changes to macroinvertebrate communities occurred upstream and downstream of the former barrier but these were transient.
3. A dramatic and sustained increase in fish density occurred immediately upstream of the barrier after its removal, but effects downstream were minor. The fish community upstream changed, largely due to rapid recruitment and dispersal of endangered European eel (Anguilla anguilla). Eel density in the formerly impounded zone increased from 0.5 per 100 m² before barrier removal to 32.5 per 100 m² 5 months after removal. By 17 months after barrier removal there was no difference in eel density across the six sections sampled.
4. Although resident stream fishes such as bullhead (Cottus gobio species complex, protected under the European Habitats Directive) were abundant in middle and upper-stream sections, brown trout (Salmo trutta, a listed species for biodiversity conservation in England and Wales) density remained low during the study and recruitment was poor. This suggests that although colonization access for anadromous trout was available, habitat upstream may have been unsuitable for reproduction, indicating that wider catchment management is required to complement the restoration of connectivity.
5. These findings suggest that tidal barrier removal is an effective method of restoring lotic habitats and connectivity, and can be beneficial for resident and migratory fishes including those of conservation importance (e.g. European eel) in coastal streams.

     

Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

Water resource development and non‐native species have been cited as primary drivers associated with the decline of native fishes in dryland rivers. To explore this topic, long‐term trends in the fish community composition of the Bill Williams River basin were studied over a 30‐year period (Arizona, USA). We sampled 31 sites throughout the basin that were included in fish surveys by Arizona Game and Fish in 1994–97 and the Bureau of Land Management in 1979–80. We found that non‐native species have proliferated throughout the entire basin, with greater densities in the lower elevations. Native species have persisted throughout most of the major river segments, but have experienced significant declines in frequency of occurrence and abundance in areas also containing high abundances of non‐native species. Next, we assessed the short‐term response of the fish assemblage to an experimental flood event from the system's only dam (i.e. Alamo Dam). In response to the flood, we observed a short‐term reduction in the abundance of non‐native species in sites close to the dam, but the fish assemblage returned to its preflood composition within 8 days of the event, with the exception of small‐bodied fish, which sustained lower postflood densities. Our findings demonstrate the importance of natural flow regime on the balance of native and non‐native species at the basin scale within dryland rivers and highlight minimal effects on non‐native fishes in response to short duration flood releases below dams.     

Seasonal and diurnal variation of downstream fish movement at four small-scale hydropower plants

Hydropower structures hinder the movement and migration of fishes, impairing their life cycles. Additionally, downstream moving fish are often at risk of being injured during turbine passage. To improve hydropower production towards more fish-friendly techniques and management, knowledge on timing and extent of natural patterns of fish downstream movement is necessary. So far, migration behaviour of long-distance migrators such as eel or salmon has been well studied, but little is known about seasonal and diurnal movement patterns of nonmigratory species or medium-distance migrators. In this study, movement patterns of 39 fish species captured by stownets while transiting hydropower facilities in four impounded rivers were assessed and compared with the fish community composition directly upstream of the hydropower plants assessed by electrofishing. Strong differences between the fish community composition inhabiting the upstream sides of the dams and the fish detected in downstream passage were evident. In each study river, the downstream moving fish community composition differed significantly between spring and autumn. On average, significantly more fish were caught during the night (2.9 fish/hr) than during the day (1.3 fish/hr). Topmouth gudgeon, European grayling and pike-perch mostly moved downstream during the night, whereas roach, spirlin and bleak were the most frequent downstream moving fish during daytime. Downstream fish movement was positively related with turbidity, water temperature and discharge. The strong differences in seasonal and diurnal fish movement patterns suggest that fish damage can be strongly reduced by adaptive turbine and corridor management, for example by shutting down turbines at peak movements.     

Biological effectiveness of an inexpensive nature‐like fishway for passage of warmwater fish in a small Ontario stream

Few studies have been conducted to evaluate the effectiveness of nature‐like fishways, particularly in low gradient warmwater streams with diverse fish communities. We evaluated a nature‐like fishway that was installed to facilitate upstream passage at a low head dam on Indian Creek near Spencerville, Ontario, Canada. A passive integrated transponder (PIT) array was used to quantify attraction and passage efficiency for 391 PIT tagged warmwater fish, represented by seven species. Attraction efficiency for the three most common species, common shiner (Luxilus cornutus), creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii), was 63.3%, 83.7% and 65.6%, respectively, and passage efficiencies were 5.1%, 38.4% and 25%, respectively. Creek chub were able to locate the fishway in less time than white sucker and common shiner; however, took longer to successfully pass. Manipulation of creek chub release locations was used to separate issues of attraction and passage and revealed that passage efficiency was highest (76.2%) for those released within the fishway and intermediate for those released at the entrance (42.1%). This multispecies fishway improved stream connectivity, but additional work is needed to fine tune its configuration. Similar projects that engage stakeholders in nature‐like fishway construction are a promising approach for the thousands of small dams that occur on low gradient streams around the globe, but those studies should incorporate a biological evaluation to ensure that attraction and passage efficiency are optimised.     

Turbine entrainment and passage of potadromous fish through hydropower dams: Developing conceptual frameworks and metrics for moving beyond turbine passage mortality

Potadromous fishes are vulnerable to involuntary entrainment through hydropower turbines. However, turbines can also provide a downstream passage route for potadromous fish. Here, we review evidence for turbine entrainment and passage in potadromous fish, and evaluate the effects of these processes on upstream and downstream populations. We develop conceptual frameworks and metrics to quantify vulnerability to turbine entrainment removals, and to quantify the efficiency of turbines as a downstream passage route. We highlight factors that influence these processes and provide case‐studies demonstrating their applicability. We found that juvenile potadromous fish are being entrained through turbines at rates high enough to impact upstream populations. Given that juvenile passage survival is often high, we argue that turbines provide an important downstream passage route for potadromous fish. We show that entrainment vulnerability is likely a function of interactions between in‐reservoir fish behaviour, habitat configuration and operations and thus not well captured by passage mortality estimates. Similarly, we show that while passage mortality can limit downstream passage efficiency, passage success is also dependent on reservoir and forebay navigation, along with survival and fitness in the downstream river. We advocate for a shift in focus away from estimates of passage mortality and injury, which have previously accounted for the majority of turbine passage research. Instead, we recommend an approach that focusses on quantification of the factors that influence downstream passage efficiency and entrainment vulnerability. Moreover, we highlight the need to better understand the broader scale impacts of these events on upstream and downstream populations.     

Living in an amphidromous world: Perspectives on the management of fish passage from an island nation

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Fish‐Net: Probabilistic models for fishway planning,design and monitoring to support environmentally sustainable hydropower

The construction of fishways for upstream and downstream connectivity is the preferred mitigation measure for hydropower dams and other riverine barriers. Yet empirical evidence for effective design criteria for many species is missing. We therefore assembled a group of international fishway designers and combined their knowledge with available empirical data using a formal expert elicitation protocol and Bayesian networks. The expert elicitation method we use minimizes biases typically associated with such approaches. Demonstrating our application with a case‐study on the temperate Southern Hemisphere, we use the resulting probabilistic models to predict the following, given alternative design parameters: (i) the effectiveness of technical fishways for upstream movement of migratory fish; (ii) habitat quality in nature‐like bypasses for resident fish; and (iii) rates of mortality during downstream passage of all fish through turbines and spillways. The Fish Passage Network (Fish‐Net) predicts that fishways for native species could be near 0% or near 100% efficient depending on their design, suggesting great scope for adequate mitigation. Sensitivity analyses revealed the most important parameters as follows: (i) design of attraction and entrance features of technical fishways for upstream migration; (ii) habitat preferences of resident fish in nature‐like bypasses; and (iii) susceptibility of fish to barotrauma and blade strike during turbine passage. Numerical modelling predicted that mortality rates of small‐bodied fish (50–100 mm TL) due to blade strike may be higher for Kaplan than Francis turbines. Our findings can be used to support environmentally sustainable decisions in the planning, design and monitoring stages of hydropower development.     

The complementary role of lentic and lotic habitats for Arctic grayling in a complex stream‐lake network in Arctic Alaska

Lakes can be important to stream dwelling fishes, yet how individuals exploit habitat heterogeneity across complex stream‐lake networks is poorly understood. Furthermore, despite growing awareness that intermittent streams are widely used by fish, studies documenting the use of seasonally accessible lakes remain scarce. We studied Arctic grayling (Thymallus arcticus) in a small seasonally flowing (June–October) stream‐lake network in Alaska using PIT telemetry. Overall, 70% of fish visited two lakes, 8% used a single lake, and 22% used only stream reaches. We identified five distinct behavioural patterns that differed in dominant macrohabitat used (deep lake, shallow lake or stream reaches), entry day into the network and mobility. Some juvenile fish spent the entire summer in a shallow seasonally frozen lake (average 71 days), whereas others demonstrated prospecting behaviour and only entered the stream channel briefly in September. Another group included adult and juvenile fish that were highly mobile, moving up to 27 km while in the 3‐km stream‐lake network, and used stream reaches extensively (average 59 days). Lentic and lotic habitats served differing roles for individuals, some fish occupied stream reaches as summer foraging habitat, and other individuals used them as migration corridors to access lakes. Our study emphasises the importance of considering stream‐lake connectivity in stream fish assessments, even to shallow seasonally frozen habitats not widely recognised as important. Furthermore, we demonstrate that individuals may use temporary aquatic habitats in complex and changing ways across ontogeny that are not captured by typical classifications of fish movement behaviour.     

Assessing the potential for fish predation to impact zebra mussels (Dreissena polymorpha): insight from bioenergetics models

Abstract –  Rates of annual food consumption and biomass were modeled for several fish species across representative rivers and lakes in eastern North America. Results were combined to assess the relative potential of fish predation to impact zebra mussels ( Dreissena polymorpha ). Predicted annual food consumption by fishes in southern waters was over 100% greater than that in northern systems because of warmer annual water temperatures and presumed increases in metabolic demand. Although generally increasing with latitude, biomasses of several key zebra mussel fish predators did not change significantly across latitudes. Biomasses of some less abundant fish predators did increase significantly with latitude, but increases were not of the magnitude to offset predicted decreases in food consumption. Our results generally support the premise that fishes in rivers and lakes of the southern United States (U.S.) have inherently greater potential to impact zebra mussels by predation. Our simulations may provide a partial explanation of why zebra mussel invasions have not been as rapid and widespread in southern U.S. waters compared to the Great Lakes region.     

Managed and natural inundation: benefits for conservation of native fish in a semi‐arid wetland system

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Effectiveness monitoring of fish passage facilities: historical trends, geographic patterns and future directions

Fishways and other passage facilities frequently prevent or delay the passage of fishes, highlighting the need for effectiveness monitoring. We reviewed the scientific literature from 1960 to 2008 reporting on effectiveness monitoring of fish passage facilities to assess what taxa and life-stages have been studied, the questions that are asked during evaluation, and how these varied over time or by geographic region. We identified 96 peer-reviewed articles of which 68% focused on passage by adult fishes. Salmoniformes was the most studied order (58% of studies). The focus of fishway evaluations did not change over the years, but varied significantly by geographic region. Studies from the tropics had a broader taxonomic scope than studies from temperate locations. Exogenous mechanisms of passage failure, such as environmental, structural and behavioural factors, were studied in 90% of studies from North America but only ∼50% of studies from Europe, South America and Australia. Endogenous (i.e. physiological) mechanisms affecting passage success were not often assessed anywhere, though they were a powerful means of evaluating mechanisms of failure. Few studies monitored migration after fish had left a facility. To improve effectiveness monitoring of passage facilities, we suggest that both endogenous and exogenous mechanisms need to be studied in an integrated fashion to understand passage failure and to inform design or operational changes that could improve passage efficiency. In addition post-departure monitoring is required to more completely assess the fitness consequences of passage.